The AM Forum

...hi from tim....i'd like to know what folks are using in their audio chain, to produce the nice smooth audio, that makes AM so nice to listen to...kinda like a poll, i assume..
...sooo..what's the deal?..

HI Tim,

This is a list of items I use on my Valiant.  I went the cheap route, if you want to call this cheap lol.  I use all Behringer equipment.

Heil PR40

T-1953 - Tube pre-amp

DEQ2496 - EQ

MDX2100 - Composer  Noise gate/Compressor

REV2496 - Reverb

Richard N6WDR

KO6NM's DAP610, and an Altec EQ to pull the high end down.

http://wa3vjb.amham.com/sound/VJBatAPE-440-8kc.mp3 (http://wa3vjb.amham.com/sound/VJBatAPE-440-8kc.mp3)

Microphone: D-104 into 10 megohm load, mixed with Electrovoice Dynamic mic. Either mic may be used alone or mixed in phase with the other.

Homebrew tube-type 2-channel audio mixer/preamp with switchable in/out pre-emphasis curve in each channel

Switchable passive low-pass audio filters: sharp cutoff @ 3400~/ more gradual cutoff @ 5000~/ flat response

Urei Modulimiter - (the only solid state unit in the audio chain) AM broadcast compressor/peak limiter

Homebrew transmitters (with 100% broadcast quality audio iron) or Gates BC1-T (160m only).

All units in the chain are interconnected via 500-ohm balanced audio line.

Microphone: An RCA 44-BX ribbon, an RCA 77-D ribbon, or an Electro-Voice RE-27 dynamic. I like the sound of the 44-BX and the RE-27 the best.

Microphone Preamplifier: Modified Ampex 351 record-playback amplifier. All triode from the input to the output. The Ampex has an unloaded microphone input transformer, which the ribbon microphones require for best performance. I also have an Ampex MX-10 tube mixer available, but I don't normally use this.

Equalizer: Rane Professional 30-band

Orban Optimod-AM Model 9100A Audio Processor, configured to roll-off at 12 Khz.

Homebrew transmitter,with 100% broadcast quality audio iron from both a Gates BC-1J and a BC-1F. The audio driver is also homebrew; it consists of a pair of class A push-pull 845 drivers in self-bias and with 1200 VDC on the plates, driven by a pair of triode-connected 6J7s, and a pair of 6J5s. HV rectification is provided by a pair of 866As. The 845s are transformer-coupled to a pair of class B 833As with shunt-regulated bias. There is 6 dB of global negative feedback from the plates of the 833As to the input stage of the audio driver.

All of my audio, from the microphone input to the input to the 845 audio driver deck, is connected via a 600-ohm balanced audio line, with full patch-bay connectivity using old WE-241 audio patchbays. Gain structures set by Daven 600/600 ohm adjustable T-pads.

73,

Bruce

I'm using a D-104 microphone, a microphone cable and a microphone connector.


Brian - W8KHZ

Sometimes a PA-42:

(http://www.jt30.com/jt30page/micpics/LaFayette%20microphone%20PA-42.jpg)

Pete,
       So thats why you always sound like you have a clothespin on your nose ;D ;D
                                                 The Slab Bacon

I have the same audio chain Brian!!  My D-104 is a "Silver Eagle"!  That makes it sound better.  ;D

73,  Jack, W9GT

Noise Cancelling Boom Electret (like Madonna)

Common Base Bipolar Preamp

TL082 Op Amp Bas Treb

6SN7 in place of mic XFMR , 6V6, 811's (ART13) and feedback

Mike WU2D

Don you have the BL40 ?
Wow that takes me back.
Did you leave the automatic phase switch in place?

A station I worked at bypassed it after we traced a certain whoomp sound to whenever it did its thing. Supposedly it switched input phase based on some sample of program material as a way to maximize assymmetry.

The line up here:

EV 27ND microphone

Wheatstone SP5 production console

Dorrough DAP 610

Class "A" audio driver in the transmitter coupled to a class "B" modulator, modulating a class "C" amplifier. I guess that makes it a "ABC" rig!

Rode K2 large diaphragm tube type condenser microphone

Collins 212B2 7 input, all tube mixer.

Orban 672A combination graphic and parametric equalizer.

Berhinger DSP 2024P Virtualizer Pro

Orban Optimod 9200AM processor

EV 27ND mic

Rane VP-12

Autogram AC-8

Dorrough DAP 310

DBX 160 to audio chain....drives ssb, AM "C"...........EQ broken.

 I'm upgrading the weak link in my audio chain by doing some voice-over training . Does that count?
                                                                 Ian VK3KRI

Marshall V-63M large diafrizm cheap chinese condenser mike, Behringer VX-2000 voice processor, bypassing the first stage of the speech amp and jacked into the second stage.

I kinda like to keep it as simple as possible. And besides the VX-2000 has more than enough knobs and switches to twiddle with to get it right!!

                                                                             The Slab Bacon

The only store-bought piece of equipment in the entire audio chain is the microphone - a Behringer B1.

Everything else is homebrew.

You *really* only need a few things to make your signal sound REALLY REALLY good.

A good mic (condenser recommended) which feeds -
a flat mic preamp, which feeds -
equalization, then feeding -
a fast attack peak limiter (this is very important), and finally feeding -
a negative peak limiter (which may be part of the transmitter, but should be included), and finally -
the transmitter frequency response should be reasonably flat with high modulation capability.

Trying to "gain limit out" the occasional high negative peaks results in an otherwise poor sounding signal because lots of peak limiting is required to do this.  Just include a negative peak limiter as part of the transmitter, or if the transmitter will pass VERY low frequencies (or DC) such as a class E, PWM, Flex, etc. transmitter, put the negative peak limiter ahead of the transmitter - but ONLY if the transmitter is a really good one - else included it *after* the modulator (perfectly valid application of a negative peak limiter).

I hear way too many overprocessed stations on the air.  Too much limiting/compression/procession *IS* distortion - it is modifying the original audio signal.  Sure, *some* peak limiting is necessary to control the dynamic range, but really, if operated correctly, the processing should be transparent and not put artifacts onto the signal or otherwise make the signal annoying to listen to after a period of time.

Just my $.02

Berhinger B1 Mic into a Berhinger mixer. side chain is a
Berhinger VX 2000 mic processor (which does just about everything!)
and a BBE Sonic Maximizer for Mic inputs...
This drives a HB speech amp, 6SJ7, 6N7, and a pair of triode connected
5881's

I only use this chain for one station.
The rest of my 8 stations, I just use a D-104, (properly phased)
into a properly designed speech amp...if 6V6's or 6L6's are used as
driver tubes, do triode connection or make sure that negative feed
back is used....
GL 73 steve
8tow

Chain?? We don't need no steenking chain!

Crystal D-104 into a 4.7 meg load -> 12AX7 amp -> 12AU7 inverter -> 6B4G x2 driver -> 810 x 2 modulator


I sound equally bad in person.  ;D

You sound fine Todd!

There is something that I have observed with many stations running all of that "audio chain" processing gear.  When they get it all adjusted to where it sounds natural and the best, it sounds just like a D-104! 
Sometimes, when adjusted to their specifications, not as good as a D-104.

73,  Jack, W9GT

B1 microphone --> VX200 --> Radio Shack solid state PA amp --> "backwards" audio output transformer --> grids of triode connected 813s

Steve QIX got me going with a Radio Shack condenser microphone suggestion a long time ago.

Take an 8" square chunk of plexiglass and drill a hole in the middle. Rear mount a condenser mic with contact cement. Mount the panel at a 45 degree angle into a wood base with rubber bumpers on the bottom.  This is what I used before the boom mic. and it sounded better but looked stupid. Come to think of it the boom mic looks stupid too.

Mike WU2D

Old Radio Shack unidirectional condenser mike - lately also a superdirectional RS mike originally meant for VCR work.

Old Radio Shack 5-band graphic EQ mike preamp - much modified filter Q and frequencies, also a series LC shunt dipping around 800Hz, that was needed for some reason.

2:1 asymmetrical peak limiter, with bass phase aligner and adjustable servo-clipper.  MPF102 JFET shunting audio for variable gain control.  3.5 KHz 2-pole Sallen-Key low-pass filter available for nighttime operation.  All solid-state.

Audio chain in TX: 7199 pentode-triode with triode operating as phase splitter driving a 12AX7 dual triode as cathode followers to the grids of two 8417s.  820 ohm 2W resistor from the screen grid of each 8417 to a 350V regulator (12BH7).  Mod transformer: Stancor A3894 wired for full pri to full secondary, orented for impedance step-up to the output.  About 8 to 10 dB of negative feedback from modulated B+ to the cathode of the pentode section of the 7199.  About 1V p-p needed for modulator input.  A small capacitor to ground from the plate of the phase splitter, to compensate for unequal leakage inductance in the halves of the mod transformer primary.  This reduces distortion above 5KHz.  (Would have been on the cathode instead, if necesssary.)

Modulated RF finals: two 6146 (A? B?), screens self-modulated with original screen resistor (20K if I recall) to unmodulated B+; only RF bypassing on the screens.  A small cap from screens, a few hundred pF, to modulated B+ to compensate for the screen RF bypass capacitance.

Modulator power supply: solid-state rectified, cap-input for about 975V for the modulator.

RF PA power supply: also solid-state rectifier, from the same winding, but original choke-input 600V for the 6146 plates.

Marshall MXL990 large con. mike
Tascam 4 channel M20 mixer w/ PE20 para EQ
Shure SE30 gated compressor/ mixer

Shure SM58 rock and roll band veteran
Fender reverb unit, the one with the springs.   Just a little reverb, now.
Bogen PA amplifier

OK, OK.  Just dreaming.  That's what I hope to have some day.  I do have the reverb tank, thanks to Rockin Joe DVD.   But the rest is just a distant plan.   Until then I squeak along with a Heil PR40 and a Symetrix 528E into a class H/class E.   I get complaints all the time.   Too clean. Really.

Jon.... I have a Bogan Amp ifn u want it ???
Below the cart machine in the rack.

Very nice looking rack.   I really do plan to build a replica of a Fender reverb unit using the reverb tank I got from N6DVD.  It's the right tank.   I think that's step one.

Jon

AF chain in which rig?

I have such an "isochordic" (tm) voice, way too assymetrical, that the biggest difference in all my audio is switching the modulator plate leads on the 32V or HB 813/811's rig (or switching mike polarization in the TR7 and other 'closed' rigs;)  heh, heh.  I can't believe the diff. when looking at the scope.  - Clean peaks way over 150% with just as clean, very quick pinch-offs one way to almost dead flat carrier and mushy valleys, long troughs (neg. mod anyone?) the other way.

So my big dream "rig" would be to have a broadcaster's voice to start with.  Yeah, a complete makeover.....

Semi seriously, I've found that the ol' D104 with a MPF102 source follower and with 8 meg. gate loading (switchable from drain to source at same 4.7k "Z bybpass" if you want) yields pretty good audio.  Then I follow that with a little 3 or 5 band EQ to make up for screen bypasses in the xmitter and similar type lossy audio leaks 'n' peaks.

The next biggest improvement is simply grounding (big strap) any mike casing directly to the transmitter.  Eliminate all ground loops. Without 120 cycle supermod, everything sounds better.  I guess a lot of this is a given with much neater audio/RF chains following but it's amazing some of the simple things I forget to do after every big change in the shack.
The 'Tron, et. al. taught me well.

Yeah, do these little things and you too can Baxter proof yur audio.  Zounds! - thread leak.  Hmm, now where're my Cannon plug thingies?

RE20 Mic
to
Behringer Virtualizer Pro Digital Effects Processor
to
CBS Labs Volumax Automatic Peak Controller
to
CBS Labs Audiomax Automatic Level Controller
to
Tube Preamp, 845's, 833's, >>>> Your Radio

Hopefully you have a nice radio and feeding a good stereo and some ears that were not blown out of your head by a Chicago concert in the early 70's.
Keith
WA1HZK
:)

That's a good point, Jack. I've never been a fan of the outboard audio chain myself, but that will change when the 300G and future BC transmitters come online. I've accumulated most of the period pieces to go with the 300G, and since it was a commercial rig, it makes good sense. I know my current audio with the D-104 is lacking a bit in base, but that's the nature of the crystal D-104 and I'm fine with it.

And, while it's true that some folks can't set up their audio to save their lives(too much bass, too little midrange, too much/little whatever), most do an excellent job. WA3VJB always sounds great here, along with K4KYV, WA5AM (ex-W5AMI), 'QIX and others. Probably the best signal here comes from W2INR, though. When G keys up the big rig, band becomes completely still, followed by smooth, clean audio (after applying the trademark 'INR' tune up, of course).

It's the gear Todd.
Mike Dorrough KO6NM has got it figured out.
I sure wish he still produced this.

Better watch who you say that to!

Chicago concert in the early 70s Keith?   Yeah and verily ;)   Even moreso - on stage while playing a gig with a band!  I'm sure Glenn NN4NY and the other musicians in the Forum can attest to this.  I just don't want to wind up like my Uncle Joe did from his band playing days - losing 70% of my hearing!  I played a bar gig, where the cops came to the bar because people could hear us across the river the bar was near, 1/2 mile away!  It turned out the sound man had the PA levels cranked for 120dB!

My audio chain at this time - primitive.  D-104 direct to a Globe Scout 680.  I may tweak it with time, and I may not (monitoring it, it sounds pretty good).  That mindset may come from my decades as a guitarist - I've reached the point where I've gotten tired of tons of outboard sound processing.  I prefer to use as little as possible to get a decent sound.

73,
Ellen - AF9J
Frustrated with the line noise, and the band going long on 75 this morning

...ELLEN...CAN YOU GO DOWN TO 3725ish?...I HEAR ALOT FROM UR AREA HERE...U SHUD TRY, IF U CAN...TIM...sk....

I'd love to Tim,

I just have to work on the VFO I won on ePay (it's a little ratty).  I plan on doing so today.  For now, I only have a 3885 crystal.  BTW, the Scout has its VFO interfaced to it through the crystal socket.  Does anybody have any idea what I can use to plug the leads into it (I don't have a spare FT-243 crystal case I can cannibalize for the job)?  PM or e-mail me with any suggestions you might have (I don't want to hijack this thread).

73,
Ellen - AF9J

Use a pair of 4-40 x 1/2" long machine screws for your crystal pins, Ellen. Solder the wires onto their heads. They'll fit perfectly.